1. Field of the Invention
The present invention relates to a lighting assembly which extends through a wall particularly, though not exclusively, for illuminating an un-manned area.
2. Description of the Prior Art
In un-manned areas such as, for example, so-called "caves" where radioactive materials are being remotely handled, it is necessary to provide a high level of illumination. Two principal types of lighting systems are used for lighting nuclear processing areas. The first is by sealed lighting units hung at stations within the cave and which are capable of being remotely disconnected and removed from the facility for maintenance as indicated schematically in FIG. 12. The second type are units inserted through the wall of the facility and have the lighting means emerging into an enclosed section with a window on the un-manned side to allow the light to shine on the area or objects to be viewed and as indicated schematically in FIG. 13.
The first type has the disadvantage that that the unit has to be removed from the radioactive area using remote handling equipment, potentially tying up scarce resources such as the in-cell crane and operators time for example. The removed unit then has to be transferred to a maintenance area for decontamination before it can be repaired, then to be reinstalled in its position within the cave using the crane again.
The second type of lighting system has an advantage over the first type in that the maintainable parts are located outside of the cave environment and there is no requirement for the use of cranes or manipulators within the cave so that processing is not interrupted nor is there any decontamination of the lighting device required which saves cost due to there being no waste arisings to be further processed. However, current designs of through-wall lighting systems of the second type have their own particular disadvantages which relate mainly to weight and safety aspects. Current designs of throughwall lights necessitate the removal of a large shielding wall plug comprising mainly concrete grout and which weighs in the region of 700 kgs. The wall plug is unwieldy and awkward to extract as the wall has a thickness of some 1-1.5 m and requires special equipment by way of a handling device weighing about 1000 kgs and specially trained personnel using a procedure which ensures that no radiation hazard is produced.
When nuclear processing facilities are built, many additional lighting units are initially installed to provide for redundancy and the fact that new light tubes will all be installed simultaneously and hence likely to fail at about the same time.
Currently, about 20 man hours are required to change a light tube in known through-wall lighting designs.
A further disadvantage of current designs is that although they have a closed cover into which the light tube emerges in use, this cover is sometimes broken accidentally by a manipulator or in-cell crane for example. Thus, when the light tube is to be replaced, it is necessary for a much more rigorous and hence time consuming and expensive procedure due to the safe-side of the wall being open to contamination by radioactive dust and debris for example.